Field of Invention
The present invention relates to a production system for vapor-grown carbon fibers (VGCF), and more particularly, to a production system for fabricating vapor-grown carbon nanofibers with high purity.
Description of Related Art
VGCF has excellent material properties of good crystal orientation, high strength, high elasticity and high corrosion resistance, a high aspect ratio, a high thermal-conductive coefficient and a low thermal-expansion coefficient. In addition, carbon fibers made by the vapor-growing method can have the structure similar to the single-crystal graphite structure, thereby forming excellent multi-wall carbon tubes having excellent electrical conductivity, wherein the thermal conductivity thereof is better than that of the thermally-conductive material such as copper or aluminum. The success of VGCF study has added quite an important product to the carbon fiber industry in which OPCF (Organic Precursor Carbon Fibers) such as PAN, Pitch carbon fibers have been the major products for quite a long time.
The VGCF production process mainly uses low boiling hydrocarbon compounds as raw material (carbon source) having pyrolysis reaction in reductive carrier gas (such as hydrogen) atmosphere, thus directly forming VGCF via the special catalysis of transition metals such as iron, nickel or cobalt in nano-particles thereof as nucleation, wherein the reaction temperature is between 800° C. and 1300° C. The VGCF fabrication process has the advantage that the fabrication skill is simple and does not need to perform the steps of spinning, pre-oxidation, carbonization, etc. required in the OPCF fabrication process, so that the VGCF fabrication process can form carbon fibers directly from cheap low-boiling hydrocarbon material via pyrolysis and catalysis.
A conventional VGCF production facility is mainly composed of a gas supplying apparatus, a reaction apparatus and a collection bin. At first, raw material gas (such as a hydrocarbon compound and a reaction catalyst) and carrier gas (such as hydrogen) enter the reaction apparatus from the gas supplying apparatus, in which a pyrolysis reaction is generated to form carbon fibers. Thereafter, the carbon fibers fall in the collection bin.
The conventional VGCF production facility has the following disadvantages: the catalyst, raw materials or carbon fibers used or produced therein are likely to adhere to an inner wall of a reaction tube of the reaction apparatus, thus forming particulate impurities or agglomerations resulting in an unsmooth flow field, or even block the reaction tube to interrupt the production; and the produced carbon fibers cannot be separated from the particulate impurities, thus causing the carbon fiber composition to include too many non-fibrous carbon impurities. The conventional VGCF contains too much non-fibrous carbon, thus decreasing the number of continuous networks to be constructed by the VGCF in the composite material to affect the performance of the composite material. Moreover, because not being highly graphitized, the conventional VGCF does not increase the performance of electrical and heat conduction as expected.
Hence, there is a need to provide a production system for vapor-grown carbon nanofibers, thereby separating carbon fibers from particulate impurities, and graphitizing the vapor-grown nanofibers, such that a VGGF (vapor-grown graphite fibers) composition with high purity is produced.